diff --git a/ghc/aclocal.m4 b/ghc/aclocal.m4
index 6eda094315..c14c83914d 100644
--- a/ghc/aclocal.m4
+++ b/ghc/aclocal.m4
@@ -613,7 +613,7 @@ AC_DEFUN([FP_SET_CFLAGS_C99],
CPPFLAGS="$$3"
unset ac_cv_prog_cc_c99
dnl perform detection
- _AC_PROG_CC_C99
+ AC_PROG_CC_C99
fp_cc_c99="$ac_cv_prog_cc_c99"
case "x$ac_cv_prog_cc_c99" in
x) ;; # noop